1. Field of the Invention
The present invention relates to a microscope which observes a sample with a pupil modulating device, for example, for phase-contrast observation, modulation-contrast observation, and differential-interference observation.
2. Description of the Related Art
Conventionally, a phase-contrast microscope and a differential interference microscope each have been known as a microscope for observing a transparent, colorless sample. Such a microscope uses a pupil modulating device to obtain an observed image with high contrast through optical diffraction and interference. For example, the phase-contrast microscope arranges as the pupil modulating device a ring slit at a conjugated position of a pupil of an objective lens, and a phase plate at the pupil of the objective lens, to observe a sample. The phase plate has a phase film which has a conjugated shape of a slit part of the ring slit, and which changes phase of direct light which is not diffracted by the sample. The phase-contrast microscope brings out contrast of the observed image by causing interference between the direct light and the diffracted light which is diffracted by the sample.
There has been disclosed a microscope which has a slider holding plural phase plates in the neighborhood of the position of pupil of the objective lens in Japanese Patent Application Laid-Open No. H7-035986. The slider of the microscope has plural openings, in which the phase plate is held in such a manner that the phase plate can be moved along a plane surface perpendicular to the optical axis. An observer slides the slider to arrange the phase plate appropriate for the objective lens in the neighborhood of the position of pupil, and operates the microscope to focus both the image of the slit and the image of the phase film at one point within the pupil of the objective lens. Specifically, the observer performs a centering operation by which the center of the slit and the center of the phase film are made overlapped with each other approximately at the center of the pupil of the objective lens.